Electromechanical actuators



1964 D. D. MUSGRAVE ELECTROMECHANICAL ACTUATORS Filed NOV. 25, 1962 feta/rd Pu/ie 3458,7536 ELECTROMECHANICAI. ACTUATOREI Daniel D. Musgrave, 8201Caraway St, Cabin .lohn, Md.

Filed Nov. 23, I962, Ser. No. 239,430 5 Claims. (till. Elli-187) This invention relates to a safety actuator of the electromagnetic type. Such devices are useful where mechanical actuation must be controlled from a distant station, as they dispense with mechanical moving parts between the control station and the actuator, using electrical conductors instead. Because of their low cost, ease of installation and simplicity, electromagnetic actuators are widely employed in military, industrial, and aeronautical equipment, and probably will be widely used in space projects- As a result of long usage and development they can be expected to function upon signal when situated in any normal environment.

Equal importance must be attached to another kind of reliability, that is, safetyagainst inadvertent function ing. This is particularly true when the control pertains to a power plant or a weapon system, for in such applications inadvertent operation may set off a disaster of catastrophic proportions. In any 1 such installation of a control actuator, careful consideration must be given to safeguards against human error, environmental conditions, and combinations of circumstances which might result in inadvertent actuation.

The hazards associated with electric actuation are difiicult to evade completely, particularly because electrical energy is not visible and under some circumstances can be transmitted Without a physical conductor. The energy levels specified for intentional actuation must be kept reasonably low to avoid excessive time lag between control and actuation. The constantly increasing usage of electric and electronic equipment provides more and more sources from which electrical energy may unintentionally be introduced into actuator circuits. 7

Important sources of extraneous electrical energy which are recognized as particularly dangerous to circuits controlling high-energy devices are lightning, static charges, galvanic action and radio-frequency energy. Very little can be done about lightning, but careful design can largely circumvent danger from static and galvanic action. The problem of radio-frequency energy is severe, particularly because modern emitters, such as radar equipment, transmit in a concentrated beam.

The above discussion pertains to typical hazards but it is not exhaustive, nor should it be considered limiting.

In consideration of the aforesaid situation, the principal object. of this invention is to provide an electromagnetic actuator which is relatively immune to typical extraneous electricity.

Another object is to provide such an actuator which will not depend on a power supply to remain in a safe condition.

Another object is to provide an actuator so designed that inadvertent changing of polarity of control conductors will not cause unintentional fuctioning.

These and other objects of the present invention will be apparent upon reference to the following specification, taken in connection with the accompanying drawings, wherein:

FIGURE 1 is a longitudinal section of an actuator which is an embodiment of this invention;

FIGURE 2 is a cross section taken in the plane indicated by numerals 2-2 on FIGURE 1;

FIGURE 3 is a graphical representation of the elec- 0 trlcal input condition for the actuator as shown in 7 FIGURES 1 and 2;

3,158,796 Patented Nov z l, 1964 FIGURE 4 is similar to FIGURE 1, but shows'displacement of some elements; 7

FIGURE Sis a cross section taken inthe plane indi cated by numerals 5-5 on FIGURE 4; y

FIGURE 6 is a graphical representationflof the electrical input condition for the actuator shown in FIGURES FIGURE 7 is similarto FIGURE 4, but with further movement of parts shown;

FIGURE 8. is a cross section taken in the plane indicated by numerals 8 8 on FIGURE 7:

FIGURE 9 is a graphical representation of the electrical input condition for the actuator as shown in FIG- URES 7 and 8;

FIGURE 10 is similar to FIGURE 1 but with springs interposed between certain operating components to vary performance characteristics; and

FIGURE 11 is a basic circuit diagram showing the actuator used in a control system.

Referring to the drawings there is shown an actuator having a housing of brass or some other nonmagnetic material I in which is journaled a rotatable shaft 3. Shaft 3 is longitudinally positioned within housing I by suitable retainers 5 and 7 which. may be shrunk on or otherwise afiixed to the shaft.

Also afiixed to shaft 3 is permanent magnet 11 from one end of which protrudes stud 13. Suitable holes are formed in magnet 11 to receive a pair of bars 15 and 17 which are parallel to shaft 3. The polarity of magnet 11 is'indicated by the letters N and S placed thereon.

Permanent magnets 19 and 21 are similar in size, shape and polar orientation to magnet 11, but they are arranged to be slidable on shaft 3 and rods 15 and 17. Because of thesimilar orientation of the several magnets, the two slidable magnets will tend to be repelled away irom the center magnet, which condition is shown in FIGURES 1 and 10.

Fixed in housing I are cores 23 and 25 which are preferably made of some material which will retain only a slight amount of residual magnetism when subjected to a magnetic field. Soft iron would be a suitable material for the cores.

Around core 23 is wound coil 27 and around core 25 is wound coil 29. i (For purpose of clarity only simplified coils are shown. The exact construction of the typical electromagnet coil is well-known andneed not be detailed V here. The relation between the winding of the two coils is shown schematically in FIGURE 11.)

As may be noted in FIGURES 2, 5 and 8, the inner ends of the cores and the ends of magnet 11 are so contoured that the magnet may rotate between the cores with a slight air gap between the fixed and moving members. Rotation in one direction (clockwise), will be stopped when stud 13 contacts core 23. A screw 31, mounted in a suitable threaded hole in housing I, is so positioned that it can act as a stop to limit rotation of magnet 11 in the other direction (counterclockwise). Two additional screws 33 and 35, also mounted in suitable threaded holes in housing 1 are positioned to limit rotation of magnets 19 and 21 respectively when these magnets are in the position shown in FIGURESI and 10. The protrusion of screws 31, 33 and into housing I canbe varied as necessary.

(The mechanical arrangement whereby magnets 19 and 21 when blocked against counterclockwise rotation by stop screws 33 and 35 prevent rotation of shaft 3 is herein referred to as latching.)

FIGURE 10 is similar to FIGURE 1 but a spring 44 has beeninterposed between magnets 19 and 11, and a similar spring 4-5 has been interposed between magnets II and 21. This alternate construction will vary the 35 functional characteristic of the actuator as explained later.

FIGURE 11 shows a primitive control circuit incorporating an actuator using the principal of this invention. The internal circuitry of the actuator is shown within housing ll. Coils 27 and 29 are in series so that the poles induced in the inner ends of cores 23 and 25 will be of opposite polarity when the coils are energized. A source of electricity 37 and a pole-changing switch are connected to the coils of the actuator by suitable leads 4]. and 43. The circuit diagram should not be considered limiting as the actuator may be used with other circuits. The pole-changing switch is shown at 39.

Operation In FIGURES 1 and 2 the actuator is shown in the standby condition. FIGURE 3 shows that there is no electrical input to the coils during standby. The mechanical output of this actuator is rotation of shaft 3 in a counterclockwise direction. In the standby condition such. rotation is blocked by magnets 19 and 21, which diverge from magnet 11 and are thereby positioned along side stop screws 33 and 35 which prevent counterclockwise rotation. (Clockwise rotation is prevented by stud 13 bearing against core 23.) The actuator can remain in standby condition indefinitely without expenditure of control energy, and without such energy, the polarity of poles P and P of the cores will be dependent on magnetic induction due to proximity of magnet 11.

When the operator decides to actuate he sends a first or unlatching pulse to the coils of the actuator. Such a pulse is shown. graphically in FIGURE 6 and it will be assumed that the direction of the pulse and the direction of winding of coils 27 and 23 is such that pole P of core 23 has become a South pole. This is indicated on FIG- URES 4 and 5 by the letter S on the pole. At the same time pole P of core 25 has become a North pole as indicated by the letter N on the pole.

The attractive force of the electromagnets is so chosen that it overcomes the repulsive force between the permanent magnets whereupon they converge as shown in FIGURE 4. It will be noted that stop screws 33 and 35 are no longer blocking counterclockwise rotation of magnets 19 and 21 but they are nevertheless constrained against such rotation by the powerful attraction of the electromagnets. (So long as this input is maintained in the coils the shaft will not be mechanically latched but it can be again latched by merely reducing the electrical input to the coils to zero.)

At any time after unlatching has been effected as described above and illustrated in FIGURES 4, 5 and 6, the operator can cause actuation by suddenly reversing the input to the coils. Such a reverse pulse is shown graphically in FIGURE 9 and the efiect it produces is shown in FIGURES 7 and 8.

The reversal of the electrical input causes the electrornagnets to exert a powerful repulsive force on the permanent magnets. As a result magnets 19 and 21 will attempt to side on shaft 3 and diverge from magnet 11. The repulsive force will also exert a torque between the electromagnets and the permanent magnets, causing the latter to pivot and thus rotate the shaft, producing mechanical actuation.

Adjusting the protrusion of stop screws into housing It varies the distance required to latch or unlatch. Sufficient travel must be provided however to permit a slight rotation before the diverging permanent magnets strike the ends of the stop screws as shown in FIGURE 7. If sufiicient travel is not provided the second pulse will cause latching action rather than rotary actuation. In FIGURE 4, it may be noted that stop screws 33 and 35 are positioned so as to provide a reasonable unlatching clearance between their inwardly protruding ends and magnets 19 and 21 respectively.

33 and 35 If an extraneous A.C. input occurs the combined eftests of inertia of the sliding magnets and inductance of the electromagnets will cause a lag in unlatching which would be of longer duration than the half-cycle time of typical alternating current. The characteristics of the electromagnets and the permanent magnets, and the length of movement required to unlatch the latter, may be so chosen that typical slow-cycle A.C. cannot unlatch the actuator.

If an extraneous D.C. input occurs, it might cause unlatching (if of proper strength and polarity) but it would have to be reversed suddenly to effect actuation as shown in FIGURES 7, 8 and 9. A slow reversal, or a powerfailure after unlatching will cause the actuator to return to the latched condition.

The springs 44 and 45 in the alternate construction shown in FIGURE 10 may be used when it is desirable to introduce a time-delay into the unlatching characteristic or when it is desired to enhance the safety of the device by requiring greater unlatching current.

The actuator could be made to function with only two permanent magnets, but the disclosed arrangement provides safety against unlatching by inertial effects of the permanent magnets if the device is subject to high G-forces along the shaft axis. In such a case one magnet will tend to remain latched due to the same force which tends to unlatch the other.

I claim:

1. An electromagnetic actuator comprising: a coil adapted for producing an electromagnetic field; a core positioned within said coil; actuating means normally retained at an inoperative position and movable to an operative position; first movable magnetic means operatively connected to said actuating means and normally magnetically attracted to said core; second movable magnetic means operatively connected to said actuating means and normally repelled from said first movable magnetic means to a first position; detent means engaging said second movable magnetic means thereby retaining said actuating means at said inoperative position; means for mounting said coil, said core, said actuating means and said detent means; and means for applying an electric current alternately in opposite directions to said coil; whereby upon a current pulse in one direction being impressed on said coil said second movable magnetic means is attracted to said core and moved to a second position whereat said second movable magnetic means is disengaged from said detent rneans; and whereby upon a subsequent current pulse in an opposite direction being impressed on said coil said first and second movable magnetic means are repel-led from said core thereby moving said actuating means from said inoperative position to said operative position.

2. The combination set forth in claim 1 further characterized by said actuating means comprising a rotatable shaft.

3. The combination set forth in claim 1 further characterized by said first and second movable magnetic means comprising similarly on'ented penm-anent magnets.

4. The combination set forth in claim 1 further characterized by resilient means interposed between said first movable magnetic means and said second movable magnetic means.

5. The combination set forth in claim 1 further characterized by said detent means being positionally adjustable whereby the extent of engagement of said second movable magnetic means therewith may be varied.

References Cited by the Examiner JOHN F. BURNS, Primary Examiner. 

1. AN ELECTROMAGNETIC ACTUATOR COMPRISING: A COIL ADAPTED FOR PRODUCING AN ELECTROMAGNETIC FIELD; A CORE POSITIONED WITHIN SAID COIL; ACTUATING MEANS NORMALLY RETAINED AT AN INOPERATIVE POSITION AND MOVABLE TO AN OPERATIVE POSITION; FIRST MOVABLE MAGNETIC MEANS OPERATIVELY CONNECTED TO SAID ACTUATING MEANS AND NORMALLY MAGNETICALLY ATTRACTED TO SAID CORE; SECOND MOVABLE MAGNETIC MEANS OPERATIVELY CONNECTED TO SAID ACTUATING MEANS AND NORMALLY REPELLED FROM SAID FIRST MOVABLE MAGNETIC MEANS TO A FIRST POSITION; DETENT MEANS ENGAGING SAID SECOND MOVABLE MAGNETIC MEANS THEREBY RETAINING SAID ACTUATING MEANS AT SAID INOPERATIVE POSITION; MEANS FOR MOUNTING SAID COIL, SAID CORE, SAID ACTUATING MEANS AND SAID DETENT MEANS; AND MEANS FOR APPLYING AN ELECTRIC CURRENT ALTERNATELY IN OPPOSITE DIRECTIONS TO SAID COIL; WHEREBY UPON A CURRENT PULSE IN ONE DIRECTION BEING IMPRESSED ON SAID COIL SAID SECOND MOVABLE MAGNETIC MEANS IS ATTRACTED TO SAID CORE AND MOVED TO A SECOND POSITION WHEREAT SAID SECOND MOVABLE MAGNETIC MEANS IS DISENGAGED FROM SAID DETENT MEANS; AND WHEREBY UPON A SUBSEQUENT CURRENT PULSE IN AN OPPOSITE DIRECTION BEING IMPRESSED ON SAID COIL SAID FIRST AND SECOND MOVABLE MAGNETIC MEANS ARE REPELLED FROM SAID CORE THEREBY MOVING SAID ACTUATING MEANS FROM SAID INOPERATIVE POSITION TO SAID OPERATIVE POSITION. 